1. Department of Physics; National Chung Hsing University; Taichung 40227 Taiwan
2. Department of Energy and Materials Engineering; Dongguk University; Seoul 100-715 Korea
3. WPI Center for Materials Nanoarchitectonics (WPI-MANA); National Institute for Materials Science (NIMS); Tsukuba; Ibaraki 305-0044 Japan
4. Department of Chemistry; Graduate School of Science and Engineering; Saitama University; Saitama 338-8570 Japan